Such spreading systems, by spreading grit in front of the wheels of vehicles, serve to increase the friction between a vehicle wheel and the ground, and hence reduce the braking distance and facilitate starting. Spreading systems are, in particular, used for rail vehicles, yet also for trucks or buses. Dry sand is, in particular, used as grit material. Yet, other suitable materials may be employed as well.
From U.S. Pat. No. 1,392,230 A, a sand spreading system for a rail vehicle is known, comprising a sand reservoir to the lower side of which a sand metering device is connected, which includes an internal passage opening that is closable by a slide. In the lower region of the sand metering device, three connections are provided to which a valve-controlled compressed-air device is associated to convey the sand to the vehicle wheels in conveyor lines.
U.S. Pat. No. 2,342,895 A describes a sand spreading device in which two conveyor lines are connected to a sand reservoir, wherein a metering device and a valve-controlled compressed-air device are provided.
From U.S. Pat. No. 2,138,526 A, a sand spreading device is known, which comprises a manifold provided in a sand reservoir and connected with three conveyor lines in a valve-controlled manner.
U.S. Pat. No. 1,776,688 A describes a spreading device comprising a sand reservoir arranged above a steam generator and connected with a duct on its lower side. A vacuum metering and conveying device transports the sand in two separate conveyor lines that end in the region of the wheels.
In the sand spreading device described in U.S. Pat. No. 3,345,097 A, a single sand conveyor line is connected to a reservoir.
U.S. Pat. No. 2,589,794 A describes a sand spreading device in which each drive wheel is connected with its separate sand metering means.
In addition, AT 403 559 B discloses a spreading device that transports the grit, particularly sand, according to the injector principle by the aid of compressed air via a suitable conveyor line to the desired location, i.e. the region immediately in front of the vehicle wheel.
EP 936 084 A2 describes a piston-controlled metering device for spreading systems, by which the metering of sand can be improved.
In conventional spreading systems, a metering device and a conveying device as well as a conveyor line are usually each associated to a grit container. For use with several vehicle wheels, the respective number of grit containers, metering devices, conveying devices and conveyor lines are required. Moreover, only relatively short conveyor line lengths have been feasible in conventional spreading systems, which is why the grit container plus metering device and conveying device have had to be arranged relatively close to the vehicle wheels. The respective system components have, therefore, been mounted in the immediate vicinity of the wheels, e.g. on the bogie of a rail vehicle, where they have been exposed not only to external influences like moisture and temperature, but also to mechanical influences.
The elevated number of grit containers plus associated components and their arrangement, for instance, in a rail vehicle also have increased mounting, maintenance and dismounting expenditures. The process of refilling an accordingly great number of grit containers, e.g. sixteen in a rail vehicle on both sides of the vehicle, has thus involved a lot of time and costs.